It has become increasingly important to accurately space insulated multiple conductors with respect to each other, and laminated or bonded flat ribbon cable has increasingly come into use for this purpose. Precise control of electrical characteristics such as impedance, capacitance, crosstalk and attenuation, especially important in digital data and signal transmission, may be thereby achieved. The control of regular spacing and irregular spacing of multiple conductors in ribbon cable form has been achieved, in the prior art, by laminating or bonding multiple conductors to a thin plastic film, such as 5 mil polyvinyl chloride (PVC) film or a 5 mil polytetrafluoroethylene film, such as that produced under the registered trademark Teflon, either by heat-bonding, adhesive bonding, or solvent bonding.
Multiple pairs of insulated twisted pair conductors have also been accurately laterally spaced in ribbon cable, by laminating multiple pairs of insulated twisted conductor pairs between, or to, thin plastic sheet or film, the twisted pairs first being laid onto a first plastic film, and either bonded to the plastic film, or retained by a second plastic film laminated to the first film. The use of twisted pairs in multiconductor cable is of great importance in the field of communications, data processing, and other applications where crosstalk in signal transmission must be kept to a minimum. In order to facilitate the connection of twisted pair cable to a mass termination device, such as an insulation displacement connector, a twisted pair multiconductor ribbon cable has been provided with intermittent straight sections, having the required accuracy in the spacing of the ends of the multi-conductor cable, as disclosed in U.S. Pat. Nos. 4,034,148; 4,096,006, and 4,202,722 owned by the instant assignee, and hereby incorporated by reference.
However, the prior art does not disclose a ribbon cable, or a method of making it, that can be made with twisted sections of indefinite length, or made in a configuration which reduces the crosstalk between conductor pairs beyond that obtainable by simply twisting adjacent cable pairs to take advantage of the common mode rejection characteristics of conventional receiving devices connected to a conductor pair, in a manner which is controllable and repeatable. As is known in the field of telephone communications, a low crosstalk cable may be made by combining a plurality of twisted conductor pairs having a variety of lays, or length of twist, and twisting the twisted pairs in groups, and twisting the groups together to form a round cable of random orientation of the conductors, it being desired to prevent any portion of one conductor from being parallel to a portion of an adjacent conductor, whereby there will be the greatest amount of electrical energy transferred between the conductors. As will be apparent, a random orientation may randomly produce high crosstalk as well as randomly produce low crosstalk, and is not appropriate for mass termination, since each individual wire must be manually untwisted and manually connected.
The invention is therefore, directed towards an improved multi-conductor ribbon cable, and a method and apparatus for making such cable, the cable having a plurality of twisted insulated conductor pairs in combination with intermittent straight sections having precise lateral spacing, and an arrangement within the twisted portion which reduces the crosstalk between adjacent pairs of insulated conductors within the twisted section, towards that obtainable from an optimized randomized round cable, while at the same time, precisely orienting the termination points of the conductors for simultaneous mass termination.